Process and composition for inhibiting and controlling microbial growth

ABSTRACT

A microbial inhibiting composition and method is disclosed. The composition comprises an amount, effective for the intended purpose of dodecylguanidine hydrochloride and 2-(2-bromo-2-nitroethenyl) furan. The method comprises administering an amount of this combined treatment to the particular water containing system for which treatment is desired.

BACKGROUND OF THE INVENTION

The formation of slimes by microorganisms is a problem that is encountered in many aqueous systems. For example, the problem is not only found in natural waters such as lagoons, lakes, ponds, etc., and confined waters as in pools, but also in such industrial systems as cooling water systems, air washer systems and pulp and paper mill systems. All possess conditions which are conducive to the growth and reproduction of slime-forming microorganisms. In both once-through and recirculating cooling systems, for example, which employ large quantities of water as a cooling medium, the formation of slime by microorganisms is an extensive and constant problem.

Airborne organisms are readily entrained in the water from cooling towers and find this warm medium an ideal environment for growth and multiplication. Aerobic and heliotropic organisms flourish on the tower proper while other organisms colonize and grow in such areas as the tower sump and the piping and passages of the cooling system. The slime formation not only aids in the deterioration of the tower structure in the case of wooden towers, but also promotes corrosion when it deposits on metal surfaces. Slime carried through the cooling system plugs and fouls lines, valves, strainers, etc., and deposits on heat exchange surfaces. In the latter case, the impedance of heat transfer can greatly reduce the efficiency of the cooling system.

In pulp and paper mill systems, slime formed by microorganisms is commonly encountered and causes fouling, plugging, or corrosion of the system. The slime also becomes entrained in the paper produced to cause breakouts on the paper machines, which results in work stoppages and the loss of production time. The slime is also responsible for unsightly blemishes in the final product, which result in rejects and wasted output.

The previously discussed problems have resulted in the extensive utilization of biocides in cooling water and pulp and paper mill systems. Materials which have enjoyed widespread use in such applications include chlorine, chlorinated phenols, organo-bromines, and various organo-sulfur compounds. All of these compounds are generally useful for this purpose but each is attended by a variety of impediments. For example, chlorination is limited both by its specific toxicity for slime-forming organisms at economic levels and by the tendency of chlorine to react, which results in the expenditure of the chlorine before its full biocidal function is achieved. Other biocides are attended by odor problems, and hazards with respect to storage, use or handling which limit their utility. To date, no one compound or type of compound has achieved a clearly established predominance with respect to the applications discussed. Likewise, lagoons, ponds, lakes, and even pools, either used for pleasure purposes or used for industrial purposes for the disposal and storage of industrial wastes, become, during the warm weather, besieged by slime due to microorganism growth and reproduction. In the case of industrial storage or disposal of industrial materials, the microorganisms cause additional problems which must be eliminated prior to the materials use or disposal of the waste.

Naturally, economy is a major consideration with respect to all of these biocides. Such economic considerations attach to both the cost of the biocide and the expense of its application. The cost performance index of any biocide is derived from the basic cost of the material, its effectiveness per unit of weight, the duration of its biocidal or biostatic effect in the system treated, and the ease and frequency of its addition to the system treated. To date, none of the commercially available biocides has exhibited a prolonged biocidal effect. Instead, their effectiveness is rapidly reduced as a result of exposure to physical conditions such as temperature, association with ingredients contained by the system toward which they exhibit an affinity or substantivity, etc., with a resultant restriction or elimination of their biocidal effectiveness, or by dilution.

As a consequence, the use of such biocides involves their continuous or frequent addition to systems to be treated and their addition to multiple points or zones in the systems to be treated. Accordingly, the cost of the biocide and the labor cost of applying it are considerable. In other instances, the difficulty of access to the zone in which slime formation is experienced precludes the effective use of a biocide. For example, if in a particular system there is no access to an area at which slime formation occurs the biocide can only be applied at a point which is upstream in the flow system. However, the physical or chemical conditions, e.g., chemical reactivity, thermal degradation, etc., which exist between the point at which the biocide may be added to the system and the point at which its biocidal effect is desired render the effective use of a biocide impossible.

Similarly, in a system experiencing relatively slow flow, such as a paper mill, if a biocide is added at the beginning of the system, its biocidal effect may be completely dissipated before it has reached all of the points at which this effect is desired or required. As a consequence, the biocide must be added at multiple points, and even then a diminishing biocidal effect will be experienced between one point of addition to the system and the next point downstream at which the biocides may be added. In addition to the increased cost of utilizing and maintaining multiple feed points, gross ineconomies with respect to the cost of the biocide are experienced. Specifically, at each point of addition, an excess of the biocide is added to the system in order to compensate for that portion of the biocide which will be expended in reacting with other constituents present in the system or experience physical changes which impair its biocidal activity.

SUMMARY OF THE INVENTION

The biocidal compositions of the present invention comprise, as active ingredients, 1) 2-(2-bromo-2-nitroethenyl) furan (BNEF) and 2) dodecylguanidine hydrochloride (DGH). These constituents are commercially available. The synergistic effect obtained by combining BNEF and DGH has not been previously disclosed.

DETAILED DESCRIPTION OF THE INVENTION

Surprisingly, the present inventors have found that mixtures of BNEF and DGH are especially efficacious in controlling the growth of fungal microbes, specifically the Trichoderma viride species. This particular species is a common nuisance fungal type found in industrial cooling waters and pulping and paper making systems.

This particular species of mold is a member of the Fungi Imperfecti which reproduce by means of asexual spores or fragmentation of mycelium. It is commonly found on fallen timber and is a widely occurring soil organism. Because of its ubiquitous nature, this mold continually contaminates open cooling systems and pulping and papermaking systems. Contamination can take the form of airborne spores or fungal mats--a mass of agglomerated hyphae bound together with bacterial cells and cemented by gelatinous polysaccharide or proteinaceous material. The slimy mass entraps other detritus, restricts water flow and heat transfer and may serve as a site for corrosion.

These fungi are able to grow in environments hositle to other lifeforms. While they are strict aerobes, Trichoderma produce both hyphae, the vegetative structure, and spores which require minimal metabolic turnover and are able to withstand harsher environmental conditions. Accordingly, by reason of demonstrated efficacy in the growth inhibition of this particular species, one can expect similar growth inhibition attributes when other fungi are encountered. It is also expected that these compositions will exhibit similar growth inhibition attributes when baterial and algal species are encountered.

In accordance with the present invention, the combined BNEF and DGH treatment may be added to the desired aqueous system in need of biocidal treatment, in an amount of from about 0.1 to about 200 parts of the combined treatment to one million parts (by weight) of the aqueous medium. Preferably, about 5 to about 50 parts of the combined treatment per one million parts (by weight) of the aqueous medium is added.

The combined treatment is added, for example, to cooling water systems, paper and pulp mill systems, pools, ponds, lagoons, lakes, etc., to control the formation of fungal microorganisms, which may be contained by, or which may become entrained in, the system to be treated. It has been found that the compositions and methods of utilization of the treatment are efficacious in controlling the fungal organism, Trichoderma viride, which may populate these systems. It is thought that the combined treatment composition and method of the present invention will also be efficacious in inhibiting and controlling all types of aerobic microorganisms.

Surprisingly, it has been found that when the ingredients are mixed, in certain instances, the resulting mixtures possess a higher degree of fungicidal activity than that of the individual ingredients comprising the mixture. Accordingly, it is possible to produce a highly efficacious biocide. Because of the enhanced activity of the mixture, the total quantity of the biocidal treatment may be reduced. In addition, the high degree of biocidal effectiveness which is provided by each of the ingredients may be exploited without use of higher concentrations of each.

The following experimental data were developed. It is to be remembered that the following examples are to be regarded solely as being illustrative and not as restricting the scope of the invention.

DESCRIPTION OF PREFERRED EMBODIMENT

BNEF and DGH were added in varying ratios and over a wide range of concentrations to a liquid nutrient medium which was subsequently inoculated with a standard volume of a suspension of spores from Trichoderma viride. Growth was measured by determining the amount of radioactivity accumulated by the cells when 14C-glucose was added as the sole source of carbon in the nutrient medium. The effect of the biocide chemicals, alone and in combination, is to reduce the rate and amount of 14C incorporation into the cells during incubation, as compared to controls not treated with the chemicals. Additions of the biocides, alone and in varying combinations and concentrations, were made according to the accepted "checkerboard" technique described by M. T. Kelley and J. M. Matsen, Antimicrobial Agents and Chemotherapy. 9:440 (1976). Following a two hour incubation, the amount of radioactivity incorporated in the cells was determined by counting (14C liquid scintillation procedures) for all treated and untreated samples. The percent reduction of each treated sample was calculated from the relationship: ##EQU1##

Plotting the % reduction of 14C level against the concentration of each biocide acting alone results in a dose-response curve, from which the biocide dose necessary to achieve any given % reduction can be interpolated.

Synergism was determined by the method of calculation described by F. C. Kull, P. C. Eisman, H. D. Sylwestrowicz and R. L. Mayer, Applied Microbiology 9,538 (1961) using the relationship: ##EQU2## where: ^(Q) a=quantity of compound A, acting alone, producing an end point

^(Q) b=quantity of compound B, acting alone, producing an end point

^(Q) A=quantity of compound A in mixture, producing an end point

^(Q) B=quantity of compound B in mixture, producing an end point

The end point used in the calculations is the % reduction caused by each mixture of A and B. ^(Q) A and ^(Q) B are the individual concentrations in the A/B mixture causing a given % reduction. ^(Q) a and ^(Q) b are determined by interpolation from the respective dose response curves of A and B as those concentrations of A and B acting alone which produce the same % reduction as each specific mixture produced.

Dose-response curves for each active acting alone were determined by linear regression analysis of the dose-response data. Data were fitted to a curve represented by the equation shown with each data set. After linearizing the data, the contributions of each biocide component in the biocide mixtures to the inhibition of radioisotope uptake were determined by interpolation with the dose-response curve of the respective biocide. If, for example, quantities of ^(Q) A plus ^(Q) B are sufficient to give a 50% reduction in 14C content, ^(Q) a and ^(Q) b are those quantities of A or B acting alone, respectively, found to give 50% reduction in 14C content. A synergism index (SI) is calculated for each combination of A and B.

Where the SI is less than 1, synergism exists. Where the SI=1, additivity exists. Where SI is greater than 1, antagonism exists.

The data in the following tables come from treating Trichoderma viride, a common nuisance fungal type found in industrial cooling waters and in pulping and paper making systems, with varying ratios and concentrations of BNEF and DGH. Shown for each combination is the % reduction of 14C content (% I), the calculated SI, and the weight ratio of BNEF and DGH.

                  TABLE I                                                          ______________________________________                                         DGH vs. BNEF                                                                   ppm      ppm      Ratio                                                        DGH.sup.1                                                                               BNEF.sup.2                                                                              DGH:BNEF     % I  SI                                         ______________________________________                                         2.5      0        100:0        91                                              1.25     0        100:0        83                                              0.63     0        100:0        38                                              1.31     0        100:0         0                                              0.16     0        100:0         0                                              0.04     0        100:0         0                                              0        40        0:100       89                                              0        20        0:100       81                                              0        5         0:100       55                                              0        1.25      0:100       12                                              0        0.63      0:100        1                                              0        0.31      0:100        0                                              2.5      40        1:16        98   1.99                                       2.5      20       1:8          98   1.61                                       2.5      5        1:2          96   1.34                                       2.5      1.25     2:1          95   1.28                                       2.5      0.63     4:1          95   1.27                                       2.5      0.31     8:1          94   1.27                                       1.25     40        1:32        97   1.44                                       1.25     20        1:16        96   1.05                                       1.25     5        1:4          93    0.76*                                     1.25     1.25     1:1          91    0.68*                                     1.25     0.63     2:1          91    0.67*                                     1.25     0.31     4:1          90    0.66*                                     0.63     40        1:64        95   1.25                                       0.63     20        1:32        91    0.87*                                     0.63     5        1:8          84    0.54*                                     0.63     1.25     1:2          79    0.43*                                     0.63     0.63     1:1          73    0.44*                                     0.63     0.31     2:1          60     0.52*                                    0.31     40        1:129       91   1.28                                       0.31     20        1:65        82   1.02                                       0.31     5         1:16        62    0.79*                                     0.31     1.25     1:4          42    0.68*                                     0.31     0.63     1:2          39    0.56*                                     0.31     0.31     1:1          21    0.83*                                     0.16     40        1:250       91   1.18                                       0.16     20        1:125       84    0.87*                                     0.16     5         1:31        69    0.51*                                     0.16     1.25     1:8          37    0.64*                                     0.16     0.63     1:4          29    0.55*                                     0.16     0.31     1:2          22    0.52*                                     0.04     40         1:1000     88   1.29                                       0.04     20        1:500       81    0.93*                                     0.04     5         1:125       59    0.66*                                     0.04     1.25      1:31        12   1.59                                       0.04     0.63      1:16         9   0.99                                       0.04     0.31     1:8           0   1.02                                       ______________________________________                                    

                  TABLE II                                                         ______________________________________                                         DGH vs. BNEF                                                                   ppm      ppm      Ratio                                                        DGH.sup.1                                                                               BNEF.sup.2                                                                              DGH:BNEF     % I  SI                                         ______________________________________                                         2.5      0        100:0        91                                              1.25     0        100:0        66                                              0.63     0        100:0        19                                              0.31     0        100:0         0                                              0.16     0        100:0         0                                              0.04     0        100:0         0                                              0        40        0:100       90                                              0        20        0:100       85                                              0        5         0:100       53                                              0        1.25      0:100       16                                              0        0.63      0:100       11                                              0        0.31      0:100        0                                              2.5      40        1:16        98   1.88                                       2.5      20       1:8          98   1.46                                       2.5      5        1:2          97   1.17                                       2.5      1.25     2:1          96   1.10                                       2.5      0.63     4:1          95   1.10                                       2.5      0.31     8:1          94   1.10                                       1.25     40        1:32        98   1.39                                       1.25     20        1:16        97   0.98                                       1.25     5        1:4          93    0.68*                                     1.25     1.25     1:1          82    0.68*                                     1.25     0.63     2:1          85    0.63*                                     1.25     0.31     4:1          89    0.58*                                     0.63     40        1:64        94   1.28                                       0.63     20        1:32        91    0.87*                                     0.63     5        1:8          81    0.55*                                     0.63     1.25     1:2          63    0.55*                                     0.63     0.63     1:1          56    0.54*                                     0.63     0.31     2:1          51    0.54*                                     0.31     40        1:129       94   1.19                                       0.31     20        1:65        89    0.80*                                     0.31     5         1:16        76    0.47*                                     0.31     1.25     1:4          28   1.19                                       0.31     0.63     1:2          25    0.92*                                     0.31     0.31     1:1          26    0.65*                                     0.16     40        1:250       93   1.12                                       0.16     20        1:125       88    0.77*                                     0.16     5         1:31        73    0.45*                                     0.16     1.25     1:8          34    0.82*                                     0.16     0.63     1:4          22    0.77*                                     0.16     0.31     1:2          23    0.49*                                     0.04     40         1:1000     92   1.15                                       0.04     20        1:500       87    0.73*                                     0.04     5         1:125       53   1.00                                       0.04     1.25      1:31        19   1.36                                       0.04     0.63      1:16        12   0.96                                       0.04     0.31     1:8           9    0.62*                                     ______________________________________                                    

Asterisks in the SI column indicate synergistic combinations in accordance with the Kull method supra, while:

1 indicates a product with 33% actives DGH and

2 indicates a product with 10% actives BNEF

In Tables I and II, differences seen between the replicates are due to normal experimental variance.

In accordance with Tables I-II supra., unexpected results occurred more frequently within the product ratios of DGH to BNEF of from about 4:1 to 1:500. Since the DGH product contains about 33% active biocidal component and the BNEF product contains about 10% active biocidal component, when based on the active biocidal component, unexpected results appear more frequently within the range of active component of DGH:BNEF of about 13:1 to 1:150. At present, it is most preferred that any commercial product embodying the invention comprises a weight ratio of active component of about 1:1 DGH:BNEF.

While this invention has been described with respect to particular embodiments thereof, it is apparent that numerous other forms and modifications of this invention will be obvious to those skilled in the art. The appended claims and this invention generally should be construed to cover all such obvious forms and modifications which are within the true spirit and scope of the present invention. 

We claim:
 1. A microbial composition comprising (a) dodecylguanidine hydrochloride and (b) 2-(2-bromo-2-nitroethenyl) furan wherein (a) and (b) are present in an amount synergistically effective to reduce the growth of fungi, the weight ratio of (a) to (b) being from about 13:1 to 1:150.
 2. The composition as recited in claim 1 wherein the weight ratio of (a) to (b) is about 1:1.
 3. A method for controlling the growth of fungi in an aqueous system which comprises adding to said system a synergistically effective amount for the purpose of a composition comprising (a) dodecylguanidine hydrochloride and (b) 2-(2-bromo-2-nitroethenyl) furan, the weight ratio of (a) to (b) being from about 13:1 to 1:150.
 4. The method as recited in claim 3 wherein the weight ratio of (a):(b) is about 1:1.
 5. The method as recited in claim 3 wherein said composition is added to said system in an amount of from about 0.1 to about 200 parts per million of said aqueous system.
 6. The method as recited in claim 3 wherein said aqueous system comprises a cooling water system.
 7. The method as recited in claim 3 wherein said aqueous system comprises a pulping and papermaking system. 